As much as 60% of all renal disease may involve a nephrotoxin. Mercapturic acid biosynthesis is an important xenobiotic detoxiciation system in mammals. The kidney plays a central role in the processing of mercapturate pathway intermediates and the excretion of the mercapturic acid. A variety of cysteine conjugates formed via the mercapturate pathway are nephrotoxic. The mechanism for toxicity of the conjugates is unclear but may involve activation by cysteine conjugate beta-lyase. However, recent data suggest that other pathways may be involved and the mechanism of toxicity may differ depending on the conjugate. Rat kidney cells in culture are a good model to study the mechanism of cysteine conjugate toxicity. Understanding the structure activity relationship for toxicity and metabolism is an important key to understanding the mechanism. Dose response relationships will be established for toxicity. Effects on cell function will be evaluated. The role of the cysteine conjugate beta-lyase pathway will be tested. The cysteine conjugate beta- lyases will be purified and the structure activity for metabolism will be determined. New pathways of cysteine conjugate metabolism will be studies and the toxicity of novel metabolites determined. Radiolabelled conjugates will be synthesized and covalent binding measured in cells and with a model protein. Selective blocking agents which block binding but do not influence metabolism will be used to investigate the role of covalent binding in toxicity. Cellular targets will be identified using the culture system. The data will be used to predict the toxicity and to study the cell biology of nephrotoxic damage and repair.